1. Field of the Invention
This invention relates to a two-dimensional dot code and a reader thereof and in particular to a two-dimensional dot code and a reader thereof for making it possible to read a dot code more accurately.
2. Description of the Related Art
In recent years, a two-dimensional dot code has been used in various fields. The two-dimensional dot code comprises a plurality of cells as basic units in two dimensions to represent a predetermined code.
Such a two-dimensional dot code in a related art often is imaged by a video camera, etc., for example, and is read from the provided image. However, to use the two-dimensional dot code imaged by a video camera and determined from the provided image, cells as basic units need to be made large to some extent because of the nature of the two-dimensional dot code. Consequently, the two-dimensional dot code itself requires a comparatively large area; this is a problem.
Then, a dot code represented using dots of the minimum units to print by a printer as basic units is proposed.
That is, the dot code is represented based on the presence or absence of dots as the minimum units that can be represented by a printer, for example, as shown in FIG. 1. Therefore, it is made possible to represent more codes in a narrow range.
However, the dot positions of such a two-dimensional dot code change because of variations in printer heads. Consequently, a dot may be printed at a print position P2 at a distance of a predetermined offset amount from an original print position P1, for example, as shown in FIG. 1. In such a case, when two-dimensional dot code is read optically by a scanner, if the offset is large, it is feared that the two-dimensional dot code may be read in error as if a dot were not printed although the dot is printed actually.
Such a read error can be prevented to some extent by enhancing the precision of a printer for printing a two-dimensional dot code or a scanner for reading the code; however, to do this, it becomes necessary to manufacture a high-precision printer or scanner, resulting in an increase in costs; this is a problem.
It is an object of the present invention to make it possible to read a two-dimensional dot code accurately without much enhancing the precision of a printer or a reader.
In a two-dimensional dot code according to the present invention, timing marks for indicating the positions of dots for representing the code is provided at at least one end on a line in a direction perpendicular to the read direction of the dots for representing the code.
A reader according to the present invention comprises first detection means for detecting the positions of timing marks placed at both ends on the lines in a direction perpendicular to the read direction of the dots for representing a code; and second detection means for detecting the dots representing the code placed between the timing marks based on the timing marks at both ends detected by the first detection means.
In the two-dimensional dot code, the timing marks for indicating the positions of dots for representing the code are placed at at least one end on a line in a direction perpendicular to the read direction of the dots for representing the code.
In the reader, the dots representing the code placed between the timing marks are detected based on the timing marks placed at both ends on the lines in a direction perpendicular to the read direction of the dots for representing the code.